A regulator circuit is a circuit which stabilizes the power supply voltage supplied from the outside, and supplies the stable output voltage to an output terminal. Load is connected to the output terminal of a regulator circuit after an output capacitor (output capacitance) is connected. Thereby, the output voltage which was stabilized in the regulator circuit and smoothed with the output capacitor is supplied to load.
In the operation of electronic devices and circuits, when the input voltage can't meet the requirements of “minimum voltage difference”, the performance of the regulator will change. In this case, the error amplifier for driving conducting element will enter fully conductive state, so that the loop gain is zero. This indicates that regulating capability of the input power supply voltage and load will become bad, and power supply rejection ratio will be substantially reduced. Therefore, the quality and performance of the regulator has become extremely important.
Closed loop negative feedback systems are commonly employed in linear integrated circuits. For instance, switching regulators use a feedback loop to monitor the output voltage in order to provide regulation. To ensure stability in any closed loop system, the Nyquist criterion must be met. The Nyquist criterion states that a closed loop system is stable if the phase shift around the loop is less than 180 degrees at unity gain. Typically, a compensation circuit is added to a feedback loop to modulate the phase shift of the feedback loop to obtain stability.
The frequency response of a linear circuit can be characterized by the presence of “poles” and “zeros.” A “pole” is a mathematical term which signifies the complex frequency at which gain reduction begins. On the other hand, a “zero” signifies the complex frequency at which gain increase starts. Poles and zeros on the left half plane of a complex frequency plane or s-plane are considered normal and can be compensated. However, poles and zeros on the right half plane of a complex frequency plane are usually problematic and difficult to manipulate. Generally, a pole contributes a −90.degree. phase shift while a zero contributes a +90.degree. phase shift. A pole cancels out the phase shift of a zero for zeros in the left half plane. In designing a closed loop system with compensation, the location of the poles and zeros are manipulated so as to avoid a greater than 180.degree. phase shift at unity gain.
In a linear circuit, poles are created by placing a small capacitor on a node with a high dynamic impedance. If the capacitor is placed at a gain stage, the capacitance can be multiplied by the gain of the stage to increase its effectiveness. Each pole has a zero associated with it. That is, at some point, the dynamic resistance of the gain stage will limit the gain loss capable of being achieved by the capacitor. Thus, a zero can be created by placing a resistor in series with the gain reduction capacitor.
The traditional linear voltage regulator circuit comprises a power transistor and an error amplifier for feedback control. This will narrow the bandwidth of the circuit due to high-gain of the error amplifier, and can't effectively response instant changes of the load current. However, if the gain is reduced and band is increased, then causing stable voltage overshoot while can't provide accurate output voltage.
In the conventional voltage regulator circuit, the stimulation unit instantly changes the load current, causing undershoot or overshoot voltage in the power source. Thus, a slow transient response in the power source affects the normal operation of the stimulation unit, thereby affecting the signal acquisition unit overall detection accuracy and with a narrow band response. Therefore, the feedback type voltage regulator is proposed.